Help settle a debate

[xptpcrewx]

Where does it say that in the code? And anyway what does that have to do with whether or not the phases are balanced? There's nothing in the code that requires phase balancing. Where in the code does it require the overcurrent devices to be the same rating.

It doesn’t “explicitly” restrict different conductor sizes unless you’re dealing with parallel sets, but you need to look at section 310.14(A)(2) and (A)(3). There is a limit to whatever benefit you’d get from having different sized conductors as part of the same circuit. It’s also very non-standard and I don’t know how you’d assign a feeder rating to the circuit or determine the minimum rating/size in 215.2. Can’t think of a good reason why anyone would want to do this. Perhaps you can tell us? It’s an interesting point though.

Getting back to the main discussion, this is in context of a load calculation regarding a single feeder (I’m guessing 3w) to the equipment and presumably one OCPD.

The line currents are not related to the delta phase currents by 1.732 for unbalanced loading. I provided the actual line currents and phase kVA in my example. It would be reasonable to size the circuit conductors and OCPD based on the largest loaded phase.

 

[petersonra]

It doesn’t “explicitly” restrict different conductor sizes unless you’re dealing with parallel sets, but you need to look at section 310.14(A)(2) and (A)(3). There is a limit to whatever benefit you’d get from having different sized conductors as part of the same circuit. It’s also very non-standard and I don’t know how you’d assign a feeder rating to the circuit or determine the minimum rating/size in 215.2. Can’t think of a good reason why anyone would want to do this. Perhaps you can tell us? It’s an interesting point though.

Getting back to the main discussion, this is in context of a load calculation regarding a single feeder (I’m guessing 3w) to the equipment and presumably one OCPD.

The line currents are not related to the delta phase currents by 1.732 for unbalanced loading. I provided the actual line currents and phase kVA in my example. It would be reasonable to size the circuit conductors and OCPD based on the largest loaded phase.

You won't get an argument from me that this is not a good idea, it's not the simplest solution, or that it's not code compliant. However that's not what you said before. You claimed it had to be done your way but the code doesn't appear to actually require what you're saying it does.

And there's no place where there's any load balancing ever required in the code. You can put everything that is a single phase load on the same phase if you want, as long as you don't overload the conductors and the overcurrent protection device is appropriate.

 

[xptpcrewx]

And there's no place where there's any load balancing ever required in the code. You can put everything that is a single phase load on the same phase if you want, as long as you don't overload the conductors and the overcurrent protection device is appropriate.

Check 210.11(B). It doesn’t apply to every type of load but it does have some balancing requirement.

 

[xptpcrewx]

However that's not what you said before. You claimed it had to be done your way but the code doesn't appear to actually require what you're saying it does.

I never suggested anyone had to do anything my way. You’re stretching that a bit. But I’m glad you made me look through the NEC to see that it could technically be done. As to the relevance of that suggestion and this discussion, it remains to be seen what benefit it would have. The way all the minimum rating/size verbiage is written is done in a way that suggests assigning one rating value to the entire feeder circuit. As far as I know, nowhere does it mention anything about looking at possible different ratings of individual conductors in a feeder circuit.

 

[GoldDigger]

The biggest obstacle to designing a feeder with unequal conductor sizes is finding a three-pole common-trip OCPD with different amp ratings for each phase. If you are not loading each conductor to near its rated ampacity, the is no motivation to using unequal wire sizes.

 

[petersonra]

Check 210.11(B). It doesn’t apply to every type of load but it does have some balancing requirement.

granted. but it is not a general requirement that loads be balanced. only those determined on a square foot basis like lighting.

 

[petersonra]

The biggest obstacle to designing a feeder with unequal conductor sizes is finding a three-pole common-trip OCPD with different amp ratings for each phase. If you are not loading each conductor to near its rated ampacity, the is no motivation to using unequal wire sizes.

I don't disagree. This is a matter of practicality, not a code requirement. Conceivably you could have fuses of different ratings.

You could also conceivably have 1 or more circuit conductors oversized but not all of them. Say you had a single phase 120 V 20 A circuit. No code reason I can think of that the hot wire could not be #12 and the N wire #10.

 

[xptpcrewx]

granted. but it is not a general requirement that loads be balanced. only those determined on a square foot basis like lighting.

No one said so. We are talking about the effects of unbalanced delta loads for calculation purposes. Not balancing of loads.

 

[xptpcrewx]

This is a matter of practicality, not a code requirement.

What about 310.10(G)(2) for parallel conductors? and 310.14(A)(2), 310.14(A)(3)? It might be a practicality issue, but its the code that renders the situation impractical with the way circuits are rated.

Conceivably you could have fuses of different ratings.

What would be the feeder rating?

You could also conceivably have 1 or more circuit conductors oversized but not all of them. Say you had a single phase 120 V 20 A circuit. No code reason I can think of that the hot wire could not be #12 and the N wire #10.

Sure, but you would be limited by the smallest conductor rating.